1. Field of the Invention
The present invention relates to a pilot valve operated demand regulator for an underwater breathing apparatus, and more particularly to such a regulator using pneumatic amplification and feedback to achieve very low inhalation effort and substantially linear relationship between inhalation effort and supplied breathable gas.
2. Description of the Prior Art
A self contained underwater breathing apparatus (scuba) typically employs a supply tank of air or other breathable gas under high pressure and a two stage regulator to provide this air to the diver. The regulator first stage is mounted at the supply tank and functions to reduce the air pressure to about 140 psi above the ambient pressure. A conduit supplies this reduced pressure air to a regulator second stage at the diver's mouthpiece. The second stage includes a demand valve system which opens to supply breathable gas in response to the inhalation effort of the diver. An exhaust port may be provided to discharge gas exhaled through the mouthpiece.
Ideally the regulator second stage should provide to the diver exactly the volume of air required, without excessive inhalation effort. The problems associated with achieving such performance are discussed in the inventor's U.S. Pat. No. 3,783,891 which discloses a balanced regulator second stage employing pneumatic amplification.
In that patented demand regulator, a balanced primary valve controls the flow of breathable gas from the supply conduit inlet to an outlet chamber leading to the mouthpiece. The primary valve is not controlled directly by a mechanical linkage to the demand-sensing diaphragm. Rather, it is responsive to the pressure differential between the inlet and a control chamber the pressure in which is established by a pilot valve linked to the diaphragm. Thus pneumatic amplification isolates the diaphragm from the flow control valve to achieve sensitive response between inhalation demand and volume of air supplied to the diver.
To achieve this performance, the patented balanced regulator includes a small orifice through the primary valve to bleed some air into the control chamber. The pilot valve includes a pilot orifice in a secondary flow path from the control chamber to the outlet chamber. This pilot orifice is selectively blocked or unblocked by a valve poppet that is linked to the diaphragm. As the diaphragm senses reduced pressure in the outlet chamber, signifying an inhalation demand, the pilot orifice is slightly unblocked to lower the control chamber pressure. The resultant pressure differential between the inlet and the control chamber causes the primary valve to open proportionately, until the unbalanced pressure force exerted on the primary valve is balanced by the bias spring force. Supplied breathable gas flows past the primary valve directly to the outlet chamber and the mouthpiece.
An object of the present invention is to provide a regulator second stage which, though utilizing pneumatic amplification, is of different configuration and simpler construction than known regulators. Another object is to provide a demand regulator which employs both pneumatic amplification and feedback to achieve low inhalation effort and a linear relationship between inhalation demand and the amount of supplied breathable gas. A further object of the present invention is to provide an improved demand regulator in which the flow of breathable gas is controlled by a main flow valve having a moveable poppet, and in which motion of the poppet is imparted pneumatically by the pressure of supplied gas under control of a pilot valve that is moounted within and carried by the moveable poppet. Yet another object is to provide a demand regulator having no pressure control chamber and requiring no bleed passage through the main valve component to a pressure control region.